This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Lifestyle factors appear to play a clinically important role in breast cancer outcome. Obesity, low levels of physical activity and high dietary fat intake have all been implicated LISA is a multicenter randomized controlled 2 arm clinical trial. The objective of the study is to evaluate if a telephone and mail-based individualized intervention program focusing on weight management can improve outcomes in postmenopausal women with early stage breast cancer. The disease-free survival (DFS), distant disease-free survival, body weight and other medical endpoints will be evaluated. Fasting blood biomarkers and tumor tissue will be tested during this trial. This trial will be conducted in Canada and three selected centers in the United States. The sponsor (Ontario Clinical Oncology Group) expect that approximately 2150 women will take part in this study. We expect 50 subjects will take part in the study in our study site. Subject population: postmenopausal women (BMI 24 to 40 kg/m2) receiving adjuvant Letrozole (Femara) for early stage breast cancer treatment. Study design: for each subject, there will be a 2 years core phase intervention (a mail-based educational intervention) and an estimated 4-6 additional years follow-up for DFS and other outcomes. During the 2 years core intervention phase, body weight and height will be evaluated at their clinical visit and blood sample for biomarker will be collected at pre-randomization and 12 month visits. Tumor tissue may be collected for testing at the time of surgery.